Two wild grasses, Zea diploperennis and Tripsacum dactyloides have been crossed to produce a novel hybrid that may improve corn by imparting beneficial characteristics including pest resistance and drought tolerance. Zea diploperennis (hereafter referred to as diploperennis), a diploid perennial teosinte and previously unknown wild relative of maize, was discovered on the verge of extinction in the mountains of Jalisco, Mexico in 1979. Diploperennis is in the same genus as maize, has the same chromosome number (n=10), and hybridizes easily with it. Tripsacum, a more distant relative of corn with a different chromosome number (n=18), has been crossed with maize by artificial means but has not been known to cross with teosinte. Many investigators believe that Tripsacum played a prominent role in the origin and evolution of maize, and that it has significant potential for improving corn by expanding its genetic diversity.
In 1984, crosses were made to diploperennis using Tripsacum pollen and U.S. Plant Pat. No. 6,906, was issued Jul. 4, 1989 on the hybrid from that cross. In Apr., 1985, the reciprocal cross to Tripsacum was made using diploperennis pollen. The plant germinated from the hybrid seed [labeled (Trip X 3-3)] developed normally, was fully fertile and produces viable fruits. This plant is referred to as Tripsacorn. The chromosome number determined from root tip counts is 2n=20 or 2n=18. There is evidence in late prophase and metaphase for chromosome fusion. Some chromosomes are linked end to end in a chain formation and others have the trisomic y-shaped configuration. Although the chromosome number is unexpected, it has been reasonably ascertained that the genotype for this plant is normal and stable.
Perennial plants have been propagated by means of cuttings and rhizome divisions. In field tests, they have produced new growth following winter temperatures of 0.degree. F. and have survived summer drought for six weeks.
In preliminary field trials of backcrosses to a commercial corn line, drought tolerance and enhanced pest resistance were observed in the F.sub.1 generation. Germination of seed from these crosses was 100%. The plants were fully fertile and there was no loss in productivity. Tripsacorn evidently provides a natural bridge for introducing Tripsacum germ plasm into corn, thereby establishing a link between these wild grasses and modern corn that may be beneficial in corn improvement breeding programs. The results of crossing Tripsacorn, labeled (Trip X 3-3), to corn were distinctly different from the results of crossing the patented plant Sun Dance, labeled (3-7X Trip), to corn. When Sun Dance was crossed to corn, the F.sub.1 plants were depauperate in growth and highly susceptible to insects and disease; whereas plants grown from Tripsacorn X corn were sturdy, more tolerant of the drought conditions during the summer of 1988, were resistant to the plant pests that plagued the corn that season, were stocky with strong stalks and more extensive root systems, were fertile and produced ears weights equal to the corn controls.
Unique propagation of Tripsacorn through successive generations by means of cuttings has demonstrated that the new plant has not only retained the continuous and abundant production capability, but also that its distinguishing characteristics hold true from generation to generation and appear to be firmly fixed. Propagation has taken place in Tennessee, North Carolina, and Mississippi.